1. Field of the Invention
The present invention relates to a brake control device, particularly to a brake control device for controlling a hydraulic brake.
2. Description of the Related Art
A conventional hydraulic brake device, as disclosed in JP-A-2002-264795, includes a hydraulic pressure source for accumulating working fluid pressure, a pressure governing valve for regulating and outputting the hydraulic pressure supplied from the hydraulic pressure source corresponding to the push-force on a brake pedal, a master cylinder that is operated by the hydraulic pressure supplied from the pressure governing valve into an auxiliary hydraulic pressure chamber, thereby generating and outputting the hydraulic pressure according to the hydraulic pressure of the auxiliary hydraulic pressure chamber, and wheel cylinders that are operated by the hydraulic pressure output form the master cylinder, whereby applying brake force to wheels of a vehicle.
Accordingly, the hydraulic pressure regulated by the pressure governing valve can provide a large brake force with a small footing-force on a brake pedal. In the conventional hydraulic brake, regenerative cooperative control switching valves are used when performing regenerative cooperative control, and the wheel cylinders communicate with the pressure governing valve or with a reservoir so as to regulate the hydraulic pressure in the wheel cylinders at an appropriate pressure.
However, in the hydraulic brake device as disclosed in JP-A-2002-264795, the hydraulic pressure output from the pressure governing valve to the auxiliary hydraulic pressure chamber decreases below a predetermined range when performing a brake action, if such a trouble occurs that a foreign substance clogged in a hydraulic pressure path on the output side of the pressure governing valve. This hinders the hydraulic pressure from being outputted in an amount corresponding to the pedal stroke amount. Consequently, in the event of such trouble, a sufficient hydraulic pressure cannot be output from the pressure governing valve to the master cylinder side.
There may also occur another trouble that a valve spool pushed into the output hydraulic pressure chamber against force of springs, by actuating the brake pedal, does not return properly even after easing the pedal because the spring is caught on the circumferential surface of the output hydraulic pressure chamber. This prevents providing an output hydraulic pressure corresponding to the brake pedal stroke amount. Consequently, a properly reduced output hydraulic pressure to be output to the master cylinder side cannot be provided.
Therefore, in order to overcome the above mentioned disadvantages, when a trouble occurs at the pressure governing valve or the like, accurate detection of the trouble and diagnosis of its situations are required so as to provide a proper action against it.
Taking the above mentioned disadvantages into account, an object of the present invention is to provide a brake control device capable of performing an accurate diagnosis on situations of the trouble on a pressure governing valve or switching valves, so as to output an appropriate output hydraulic pressure corresponding to a brake pedal stroke amount even if a trouble occurs on the pressure governing valve or the switching valves.